The conventional practice to stiffen outer automotive body panels is with a sheet thermoset polymer placed on the inside of a panel and then heat cured in a paint oven. The conventional heat cured stiffener is applied as a wallpaper sheet type applique or as a sprayed on layer. The applique is provided in a single or double layer sheet. The main layer is a thermoset layer with or without a backing. Where a backing is used, the backing can be fiberglass cloth, metal screen, or foil. The spray on is a single polymer layer without a backing. The polymer layer is generally 0.020 to 0.100 inches thick.
In the automotive industry when the vehicle doors are painted during heat cure there is a problem with paint read through due to the heat curing of the outer metal body panel stiffener and the expansion and contraction of the metal outer panel during the paint bake cycle. It would be desirable if some techniques could be provided to eliminate or reduce the paint read through problem.
An object of this invention is to provide a body panel stiffener which improves upon the conventional practices.
A further object of this invention is to eliminate paint shadowing or metal distortion by reducing the cure shrinkage strains during the polymer cure and metal panel curing.
A still further object of this invention is to provide such techniques which are particularly adaptable for the automotive industry.
In accordance with one aspect of this invention a laminate body panel reinforcement or stiffener is provided which includes two polymer layers mounted against a substrate with or without a backing. Preferably, one of the polymer layers is a compliant foam which would be disposed directly against the substrate or structural member being reinforced. An outer or rigid foam layer is secured to the other side of the compliant foam layer and a carrier, such as a foil or fibreglass backing is secured to the outer surface of the rigid foam layer.
In accordance with another aspect of this invention the reinforcing laminate for a part or substrate is made from a stiffener member or backing having an expandable foam secured thereto. In accordance with the invention read through is controlled by various alternative techniques. For example, the read through can be controlled by having no parallel longitudinal edges. This can be achieved by having either wavy and/or saw tooth conditions on two and/or four opposing edges. A further technique to control read through would be by the material polymer thickness and by punching or forming holes through all the polymer and backing layers. The hole pattern can be ordered or uniform or can be in a staggered or a random display.